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Nuclear receptor subfamily 1, group I, member 2

SAR, pregnane X receptor

This gene product belongs to the nuclear receptor superfamily, members of which are transcription factors characterized by a ligand-binding domain and a DNA-binding domain. The encoded protein is a transcriptional regulator of the cytochrome P450 gene CYP3A4, binding to the response element of the CYP3A4 promoter as a heterodimer with the 9-cis retinoic acid receptor RXR. It is activated by a range of compounds that induce CYP3A4, including dexamethasone and rifampicin. Several alternatively spliced transcripts encoding different isoforms, some of which use non-AUG (CUG) translation initiation codon, have been described for this gene. Additional transcript variants exist, however, they have not been fully characterized. [provided by RefSeq, Jul 2008] (from
NCBI)

The study of the host genetic background of Pregnane X Receptor (PXR; NR1I2) and Constitutive Androstane Receptor (CAR; NR1I3 and NR1I4), represents a new and attractive strategy to discern variability in ADME of antineoplastic drugs.

In this study we have delineated the structure-activity relationship (SAR) for these different targets and correlated them to that required for anticancer activity and determined that Des1 inhibition is primarily responsible for the antiproliferative effects of SKI-II and its analogues.

The quinolone eukaryotic SAR is comprehensively discussed, contrasted with the corresponding prokaryotic data, and merged with recent structural biology information which is now beginning to help explain the basis for that SAR.

Ultimately, seminal studies by many investigators led to the discovery of several bile acid-activated receptors including the farnesoid X receptor, the vitamin D receptor, the pregnane X receptor, TGR5, α5 β1 integrin, and sphingosine-1-phosphate receptor 2. Several of these receptors are expressed outside of the gastrointestinal system, indicating that bile acids may have diverse functions throughout the body.

UNASSIGNED: The pregnane X receptor (PXR) has been well-established as a critical mediator in regulating important drug metabolizing enzymes and transporter proteins, including cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp).

Here, using a pregnane X receptor (PXR)-humanized mouse model, we found that co-treatment with RIF and INH causes accumulation of the endogenous hepatotoxin protoporphyrin IX in the liver through PXR-mediated alteration of the heme biosynthesis pathway.

Results provide a way to development of a dual PXR agonist/FXR antagonist with a robust immunomodulatory activity and endowed with the ability to modulate the expression of bile acid-regulated genes in the liver.